Industrial production of intermediate food product (i.f.p.) based on fish flesh and packaged i.f.p.s. thus produced

ABSTRACT

The invention relates to the production of hydrated concentrates of myofibrillar proteins from fish flesh which are commonly known as surimi-base or, more generally, intermediate food products (I.F.P.). The inventive production method comprises the following successive steps: (1) initial minced fish flesh is prepared from fish fillets; (2) said initial mince is washed with water until a washed mince is obtained which contains a residual fraction of sarcoplasmic proteins and lipids of between 0.1 and 3% of the weight of the mince; (3) whilst wet, the washed mince is refined by eliminating a fraction of impurities; (4) the refined mince is mixed until an even emulsion mince is produced; (6) the emulsified mince is drained so as to produce a densified mince; (7) cryoprotectants are then added to the densified mince in order to form a final freezable mince; (8) the final mince is packed in nutrient plates; and (9) said plates are frozen. In this way, a quality I.F.P is obtained with a significantly increased production yield in relation to the prior art, particularly for fatty fish.

The invention relates to the field of the food industry and moreparticularly to the field of the production of surimi-base and otheranalogous intermediate food products (IFPs) prepared from fish flesh.

It is noted that surimi-base is a generic term for a hydratedconcentrate of myofibrillar proteins which is obtained from fish fleshthat has been minced, washed, strained and centrifuged several times toproduce a protein gel used in the manufacture of kamaboko and otherderived products.

The traditional process for the manufacture of surimi-base has existedsince the 15th century and various improvements have been made to thisbasic technology, either to improve the production yields or to improvethe physical characteristics (gelling strength, whiteness, elasticity,stability) of the product.

Irrespective of the methods described below, the inventors' objectivewas always to perfect the methods of separating and extracting themyofibrillar proteins from fish flesh, said proteins alone beingresponsible for the quality of the surimi-base, and to optimize theremoval of the pro-oxidizing or denaturing agents.

It should actually be stated that although the myofibrillar proteinsalone are responsible for the desired qualities of the surimi-base, theother substances naturally present in fish flesh, for example the lipidsand the sarcoplasmic proteins, modify the functional properties of themyofibrillar proteins and cause a denaturation of the finished product(surimi-base).

Surimi-base is currently prepared mainly from “lean” or “white” fish,such as hake, coalie or whiting, essentially because their tissuescontain a high proportion of “white” muscles rich in myofibrillarproteins and a low proportion of “red” muscles rich in lipids andpro-oxidizing elements.

These “white” fish, which are sought not only for the production ofsurimi-base but also for traditional uses (whole or as fillets, fresh orfrozen) and whose exploitable stocks have long renewal dynamics, arevery often overexploited and subjected to catch quotas. Theseestablished bioeconomic facts have a significant effect on the costs ofaccessing the resource, resulting in seasonal speculations that arerather inappropriate for a long-term industrial business strategy.

On the other hand, so-called “oily” fish, such as scad, sardine ormackerel, contain a high proportion of “red” muscles and lipids, makingthem difficult to use for the production of surimi-base for the reasonsreferred to above.

Attempts have nevertheless been made to use these “oily” fish in thesurimi-base industry because of their abundance, the fast rate ofrenewal of their exploitable stocks, and their low commercial value.

However, converting the known processes for the manufacture ofsurimi-base from “lean” fish to “oily” fish requires that the flesh bewashed and refined more thoroughly to remove the excess lipids, pigmentsand sarcoplasmic proteins. These successive operations cause significantlosses of production yield and consequently result in a low economicviability.

Secondly, and as a general principle, the processes known or proposedhitherto for the manufacture of surimi-base take no account of thespecific characteristics of the raw material, namely the fish. Now,important variations in the biochemical composition of the fish fleshare observed according to the species fished, the fishing season and themethod of catching and storing the fish before treatment, and thesevariations cause fluctuations in the quality of the finished product(surimi-base). On the whole, the quality of a surimi-base for a givenprocess is directly dependent on the specific characteristics of thefish from which this surimi is manufactured.

Thus, in a first existing process, the headed, gutted and filleted fishare introduced manually between two drums, one of which is in the formof a screen (sieve) enabling the muscle tissues to be separated from thebones and the epidermal tissues as a function of a pressure gradient.

The pulp obtained contains variable proportions of sarcoplasmicproteins, myofibrillar proteins, connective tissue proteins, lipids anddiverse impurities.

This crude pulp is then subjected to a series of washes with water,followed by centrifugations, to remove the soluble proteins and thelipids.

The third step of this process consists in pressing the pulp to removethe excess water and produce a pulp with a water content of about 80%.

The fourth step consists of a refining phase aimed at removing theconnective tissues contained in the pulp. The refining is performed dryin this process. The product is subsequently shaped into blocks and thenfrozen after being mixed with various cryoprotectants.

A second process for the manufacture of surimi-base comprises continuouswashing of the pulp, followed by centrifugal decantation or pressingbefore refining so as to gain better control over the moisture contentof the finished product. Different variants of this system have beenproposed in which these various steps are differently ordered andalternated.

However, these processes of the prior art do not allow a total removalof the connective tissues and the impurities, such as the skin debris,which have to be removed prior to the manufacture of kamaboko, the mainreason being that dry refining does not make it possible to strain thepulp with sufficiently small holes without clogging or without theproduct warming up. In addition, pressing the pulp causes a significantloss of yield due to a random and imprecise dehydration of the pulp.

A third process, described in document FR 2.651.967, made it possibleappreciably to optimize these production methods by carrying out arefining operation in a very wet medium, followed by a centrifugaldecantation.

This refining in a wet medium (minimum water content of 92%) has theadvantages of:

-   -   removing the “red” muscle containing sarcoplasmic proteins and        heat-resistant proteases. In fact, when refining in a wet        medium, there is no equilibrium between the fish flesh and the        washing medium, and the constituent elements of the flesh react        differently. The proteins of the “white” muscle swell and form a        product intermediate between a gel and pulp, which can pass        through a sieve having perforations in the order of 1 mm,        whereas the proteins of the “red” muscle hydrate less and remain        firm, preventing passage through the sieve.    -   facilitating the dislocation of the structures of the fat cells        and consequently improving the removal of the lipids.    -   facilitating the removal of the connective tissue fibers and the        impurities.

Although this third process is applicable to any type of fish,particularly so-called “oily” fish, in that it affords a betterpurification of the pulp and a better removal of the pro-oxidizing ordenaturing agents, it nevertheless has the disadvantage, in common withall the techniques of the prior art, of causing substantial reductionsin the production yields in proportion to the number ofwashing-centrifugation sequences and the degree of refining.

In summary, the principle of the prior art is above all to look for anymeans of removing the sarcoplasmic proteins, lipids, pigments and otherpro-oxidizing substances and, by removing these elements, to avoid anyprotein/protein or lipid/protein interaction responsible for thedenaturation of the finished product (surimi-base).

The first object of the invention is to propose a process for theproduction of surimi-base and other intermediate food products from anytype of fish, said process being adaptable according to the nature andspecific characteristics of the fish used and according to the desiredfinal quality of the product.

Another object of the invention is to propose a process for theproduction of surimi-base and other intermediate food productsparticularly from “oily” fish, for which the production yield isimproved in relation to the prior art.

To this end the invention relates to a process for the manufacture ofhydrated concentrates of myofibrillar proteins from fish flesh, whichare commonly known as surimi-base or intermediate food products, saidprocess comprising the following steps in succession:

-   -   first of all, an initial pulp of minced fish flesh is prepared        from fish fillets;    -   said initial pulp is then washed with water until the residual        fraction of lipids and sarcoplasmic proteins in the washed pulp        is between 0.1 and 3% of the weight of the pulp;    -   the washed pulp is then refined in the wet state by removing a        fraction of impurities;    -   the refined pulp is then mixed until it is in the form of a        homogeneous emulsion;    -   the emulsified pulp is then drained to produce a densified pulp;    -   cryoprotectants are then added to the densified pulp to form a        final pulp suitable for freezing;    -   the final pulp is then packaged in the form of nutrient blocks;    -   and said blocks are frozen.

As will become even more clearly apparent below, the inventionessentially consists in retaining a certain lipid and protein fractionduring the washing and treatment of the fish pulp and in subsequentlyneutralizing the oxidizing or denaturing potential of these residuallipids and proteins.

According to one preferred mode of carrying out the invention, thepulping operation is coupled with the addition of water. Preferably, thewater is added in a ratio of at least one volume of water to threevolumes of pulp.

The pulping operation is preferably carried out as a function of adensity gradient of the material, making it possible to distinguishbetween different fractions.

One preferred embodiment of the invention will comprise a washingoperation composed of the following steps:

-   -   Water is added to the initial pulp and the whole is mixed to        form a water-pulp mixture.    -   The water-pulp mixture is centrifuged and the resulting water is        removed.    -   The centrifuged pulp is washed continuously with water.

Preferably, in the centrifugation step, the volume of water removed isbetween 80 and 95% of the volume of water initially used.

The mixing operation is preferably carried out continuously until thepulp is in the form of an emulsion with a stability of more than 10minutes.

In another preferred mode of carrying out the invention, the continuousmixing step is followed by a deodorization of the homogenized pulp inwhich the latter is evacuated.

In one preferred embodiment of the invention, the operation for drainingthe emulsified pulp will be carried out by centrifugal decantation.

In another preferred mode of carrying out the invention, the final pulpis subjected to a cold extrusion operation when the cryoprotectants areadded.

The invention further relates to an installation for carrying out theprocess defined above, said installation comprising the followingelements successively assembled in series in the order shown:

-   -   a pulping device also provided with a waste recovery trough;    -   a pulp washing device provided with a system for discharging the        wash waters;    -   a pulp refining device provided with a system for discharging        the fraction removed;    -   a continuous pulp mixing device;    -   a pulp draining device provided with a system for discharging        the liquid fraction;    -   a device for adding cryoprotectants to the pulp;    -   a device for forming the nutrient blocks;    -   and a device for freezing the nutrient blocks.

In one preferred mode of carrying out the invention, the pulping deviceconsists of a cylindrical sieve having perforations of differentdiameter according to a linear gradient ranging from 0.2 to 0.4 mm, andof a variable-pitch endless screw conveyor placed inside said sieve,which is provided upstream with a hopper.

Preferably, the washing device consists of the following in succession:

-   -   a refrigerated double-chamber tank equipped with a pipe for the        addition of water, if required, and with mixing equipment at the        bottom and over the entire height of the tank;    -   a screen centrifuge;    -   and a continuous washing device consisting of a refrigerated        double-chamber cylindrical tank equipped with a pipe for the        addition of water, and with mixing equipment.

Advantageously, the pulp mixing device is a static continuous mixer ofthe LPD (low pressure drop) type.

In one preferred mode of carrying out the invention, there will also bea deodorization-device located behind the continuous mixing device.

Preferably, the pulp draining device is a centrifugal decantationdevice.

In one preferred mode of carrying out the invention, there will also bea cold extrusion device allowing the addition of cryoprotectants.

Preferably, the cold extrusion device consists of the following insuccession:

-   -   a conveyor of the hooded screw conveyor type;    -   a controlled-throughput ram;    -   and a double-screw extruder equipped with means for monitoring        and regulating the pressure.

The invention further relates to the surimi-base obtained by theabovementioned process from oily fish such that its residual fat contentis between 0.1 and 1.5%.

Advantageously, the oily fish can be sardine, scad, mackerel orsardinella.

The various essential points on which the invention is based will betaken individually and explained below, but the invention will first beclearly illustrated by means of the description of the following examplegiven with reference to the attached plates of drawings, in which:

FIG. 1 is a block diagram showing the flow sheet of the treatmentaccording to the invention;

FIG. 2 is a diagram of the installation for carrying out the invention;

FIG. 3 is a curve showing the variation in the production yield (Y) ofsardine surimi-base from whole fish (percentages by net weight) as afunction of the percentage of residual lipids (RL) microencapsulatedwithin the protein matrix;

FIG. 4 is a curve showing the variation in the gelling strength gradient(GS) of the sardine surimi-base as a function of the percentage ofresidual lipids (RL) microencapsulated within the protein matrix.

The process will now be described with reference mainly to FIGS. 1 and 2(unless expressly indicated otherwise), observing the chronologicalorder of the constituent operating steps (or phases). It is applicableto any type of fish (oily or non-oily, freshwater or seawater) at anyperiod of its natural cycle.

Phase 1: Pulping (1)

The pulp is obtained by means of a pulper 101 in which the material issubjected to a gradual linear separation as a function of a densitygradient along a drum having several perforation diameters. Thisseparation as a function of density and texture makes it possible tooptimize the separation of the muscle tissues from the subcutaneousadipose tissues and from the bones and skin.

The headed and gutted fish A (without peritoneum), filleted- ornon-filleted, is introduced into a hopper and taken up by avariable-pitch endless screw conveyor inside a cylindrical sieve havingperforations ranging from 0.2 to 0.4 mm. A gradual separation of theconstituent elements of the material introduced is obtained as afunction of the density of the tissues, the diameter of the perforationsand the compression stresses generated by the endless screw. One or morefractions of material will be retained according to the qualityspecifications applied to the finished product (surimi-base—intermediatefood product).

Again in contrast to the prior art, this step is followed by theaddition of process water C immediately at the outlet of the rotatingsieve in proportions of 1 to ⅓ (⅓ volume of water to 1 volume of pulp)by means of a valve 127. This immediate addition of water improves thesolubilization of the sarcoplasmic proteins, whose dilutability isoptimal as from the first few seconds of mixing of the pulp.

The process water will be prepared in a double-chamber tank 117 from thepurest possible fresh water, whose hardness will be adjusted to 13° H(French degrees of hardness)—equivalent to 130 mg/l of calciumcarbonate—and its temperature will be in the order of 5° C. The pH ofthe process water may be adjusted so that the fish pulp remains asneutral as possible and so that the natural oxidation phenomenaoccurring after the rigor mortis phase of the fish can be counteracted.

A device consisting of a tank 118 and a metering valve 131 supplies thefresh water. A device consisting of a tank 119 and a metering valve 130enables the salinity of the process water to be regulated. A deviceconsisting of a tank 120 and a metering valve 129 enables the pH of theprocess water to be regulated. A device consisting of a tank 121 and ametering valve 128 enables the concentration of conditioning agent inthe process water to be regulated. The temperature of the process wateris maintained at 5° C. by means of a plate exchanger 125.

This technique allows a continuous mechanized treatment without theindividual fish fillets being introduced manually into the pulpingmachine, which, to the knowledge of the Proprietors, was not possible inthe prior art.

When this step is complete, the pulp B, with added water, is recoveredby means of a pump 116 g, and a waste fraction D is discarded into astorage trough 139. The pump 116 g is associated with a flow regulatingvalve 134 g and a discharge valve 135 g.

Phase 2: Washing (2)

The washing operation has to allow the retention of a given fraction oflipids and sarcoplasmic proteins of between 0.1 and 3% of the totalweight of the pulp. It is carried out by means of a washing device 102.This washing device 102 is associated downstream with a device 124 formeasuring the residual lipid content, which consists of an online sensoror a unit that takes samples for laboratory analysis. According to theinvention, the washing operation proceeds in three steps:

Step 1: Washing by Mixing and Buffer Storage (10)

The pulp B is introduced into a refrigerated double-chamber tank 110equipped with a mixing device at the bottom of the tank and over theentire height of the tank.

Process water C, whose physicochemical characteristics are identical tothose of the process water of phase 1, is added until a proportion ofone volume of water (R1) to one volume of pulp (ratio 1:1) is reached.

The product is mixed at a speed of 20 to 90 rpm for a period notexceeding ½ hour. The duration of this washing/buffer storage depends onthe initial quality of the product.

Step 2: Centrifugation (11)

The water-pulp mixture E is pumped continuously by means of a pump 116 ais introduced into a screen centrifuge 111. The pump 116 a is associatedwith a flow regulating valve 134 a and a discharge valve 135 a.

The pulp passes into a perforated cylindrical sieve (diameter ofperforations 0.5 mm), where it is centrifuged by a system of rotatingblades. Preferably, the equipment should operate according to the testbench standards to give the following results: flow rate of 300 to 400l/hour for a sieve of diameter 20 cm and length 25 cm and for a bladerotation speed of 250 rpm.

The water G, charged with soluble proteins and fats, passes through thesieve and is discarded by means of a discharge device 140. Preferably,the amount of water recovered (R2) should be adjustable to a value ofbetween 80 and 95% of the initial amount added in phase 1 and step 10,i.e. on average R2=90%×R1.

Step 3: Continuous Washing (12)

The centrifuged pulp F is transported by means of a pump 116 b to arefrigerated double-chamber cylindrical tank 112 (refrigeration isomitted if there is no observed temperature increase under the specificuse conditions) equipped with a mixing device preferably consisting ofcylindrical fingers of diameter 2.5 cm, whose length is such as to allowa 0.5 to 1 mm gap between the blades and the skirt. The pump 116 b isassociated with a flow regulating valve 134 b and a discharge valve 135b.

Process water C is added until the volume is preferably equal to R3(=R1+R2).

Preferably, the mixing is effected at a variable speed of 30 to 200 rpm.This washing operation is continuous.

Phase 3: Refining (3)

The washed pulp H, with added water (moisture content between 88 and95%), is transferred to a refiner 103 by means of a pump 116 c. The pump116 c is associated with a flow regulating valve 134 c and a dischargevalve 135 c.

The pulp passes into a perforated cylindrical sieve (diameter ofperforations 1 mm), where it is centrifuged by a system of bladesrotating at high speed. The pulp is forced through the sieve. The mostsolid parts remain inside the sieve and are discarded. Preferably, theequipment should operate according to the test bench standards to givethe following results: flow rate of 100 l/hour for a sieve diameter of14 cm and length of 19 cm and for a blade rotation speed of 1000 to 1500rpm.

The priority function of this refining is to remove the connectivetissue fibers and the residual skin debris. The variation incentrifugation speed makes it possible gradually to remove all or partof the red muscles present in the pulp. The final lipid concentration isadjusted in this step.

The waste fraction K is discarded through a discharge device 142.

Phase 4: Continuous Mixing (4)

The refined pulp J is introduced under low pressure by means of a pump116 d into an online static mixer 104 composed of mixing elements of theLPD (low pressure drop) type. The pump 116 d is associated with a flowregulating valve 134 d and a discharge valve 135 d.

This static mixer consists of one or more tubes having internal baffles(two semi-elliptical diaphragms intersecting at the center at an angleof 90°) arranged so as to allow homogeneous mixing of the pulp (emulsionstability more than 10 minutes). The mixing is based on division andtransverse deflection of the fluid. For laminar flow, the number ofsubdivisions L generated by E elements with N components to be mixed isgiven by the formula L=N(2)^(E). For turbulent flow, the elementsaccentuate the accidental dispersion of the microfluxes. This mixingallows a rapid diffusion of the soluble proteins and a mechanicalseparation of the fats, which end up in a stable aqueous emulsion.

This emulsion makes it possible to microencapsulate the denaturingelements, such as the lipids, within the protein matrix and prevents anyinteraction between the constituents of the mixture.

Phase 5: Deodorization and Evacuation (5)

The stable emulsion of fish pulp L is transferred by means of a pump 116e to a deodorization device 105 consisting of a refrigerateddouble-chamber tank connected to a vacuum pump 122 for obtaining apressure reduction of at least 0.8 bar, and equipped with a slow mixingsystem (20 to 90 rpm). The pump 116 e is associated with a flowregulating valve 134 e and a discharge valve 135 e. The vacuum pump 122is associated upstream with a flow regulating valve 136 and a dischargevalve 137 and downstream with a filter 144.

Evacuation makes it possible to remove the volatile compounds N which,in the prior art, are responsible for the residual flavor of thefinished product (surimi-base).

Phase 6: Centrifugal Decantation (6)

The homogenized and deodorized fish pulp M is transferred by means of apump 116 f to a constant-flow centrifugal decanter 106 consisting of acylindro-conical bowl housing a screw conveyor. The pump 116 f isassociated with a flow regulating valve 134 f and a discharge valve 135f.

The product to be treated is introduced into the feed chamber of therotating assembly by means of a fixed feed pipe located in the axis ofrotation of the bowl. This chamber allows a uniform distribution of theproduct.

Under the action of the centrifugal force, the solid phase is flungagainst the wall of the bowl. The solids are transported by the screwconveyor to the conical part of the bowl, where they are extracted fromthe liquid phase and discharged continuously towards the next step. Theclarified liquid P (waste) is discharged by overflowing through orificeslocated at the cylindrical end of the bowl, and then discarded by meansof a discharge system 143.

The objective is to reduce the moisture content of the product to withina range of 74-84%.

Phase 7: Addition of Cryoprotectants and Cold Extrusion (7)

The decanted pulp O is taken up by means of a hooded screw conveyor 113,or by pumping, and introduced into a cold extruder 115 with co-rotatingtwin screws.

The extruder 115 is fed with pulp by a controlled-throughput ram 114which meters a precise weight. A back pressure valve 126 isadvantageously placed at the outlet of the extruder 115 for varying theextrusion parameters. According to the invention, the conveyor 113—ram114—extruder 115—back pressure valve 126 assembly constitutes the coldextrusion device 107.

A device 123, associated with a metering valve 138, makes it possible toadd three pulverulent cryoprotectant additives Q in the followingproportions: sugar: 4%; sorbitol: 4%; polyphosphate: 0.1%.

The pulp is carried along by a double screw over which transfer, mixingand shear elements are distributed to produce an optimal disorganizationof the muscle fibers and give the finished product (surimi-base) itsgelling properties.

The objective of this microdestructuring, apart from allowing intimatemixing with the cryoprotectants, is to increase the number of potentialprotein reattachment sites by forming a continuous and orderedthree-dimensional protein network.

This extrusion phase should be executed under controlled temperatureconditions so as to avoid both a denaturation of the proteins and asolidification of the pulp in the extruder barrel.

Phase 8: Forming of the Blocks (8)

The pulp R is recovered continuously at the outlet of the extruder andintroduced into a block forming device 108, where it is formed intoblocks S of thickness 5 to 10 cm and weight 10 or 20 kg, and thenpackaged in opaque polyethylene bags.

Phase 9: Freezing (9)

The packaged blocks S will be cooled as quickly as possible afterextrusion (with a delay of not more than 30 minutes at 4° C.) to atemperature below −5° C. so that the product preserves all itsproperties. The preferred freezing device 109 will operate by contactfreezing. The frozen blocks of surimi T are now ready to use.

By way of example, such a production installation will have an input of1400 kg per hour of fish fillets and an output of 720 kg per hour ofready-to-use packaged surimi.

Another example is given in the Table below, which follows the weight ofthe different phases (oil, solid, water) contained in the materialthroughout the process according to the invention. The 2400 kg of fishfillets initially introduced were obtained from 4000 kg of whole fish.The production rate is 2400 kg of fillets introduced per hour. Thisexample does not include the deodorization phase (5). Water Solid TotalOil (kg) (kg) (kg) (kg) Introduction of 2400 kg of 288 1752 360 2400fillets Mixing (10): Addition of 2400 kg 288 4152 360 4800 of waterCentrifugation (11): Removal 15 2380 245 2640 of 2160 kg of wash waterContinuous washing (12): 15 6880 245 7140 Addition of 4500 kg of waterRefining (3): Removal of 1345 kg 13 5573 209 5795 of water andimpurities i.e. 0.2% Continuous mixing (4): — 5573 222 5795Emulsification Centrifugal decantation (6): — 900 210 1110 Removal of4685 kg of liquid Extrusion (7): Addition of 90 kg — 900 300 1200 ofcryoprotectants i.e. 75% i.e. 25%

It is seen that the retention of 0.2% of oil after the refiningoperation (3), and its incorporation into the solid phase bymicroencapsulation in the protein network through emulsification,ultimately produces 1200 kg of surimi. This amounts to a yield of 30%based on the weight of fish used, or 50% based on the weight of filletsintroduced.

It is self-evident that these examples do not imply a limitation. Thus,the deodorization (5) of the pulp is a preferred mode of carrying outthe invention, but can be omitted. Likewise, the cold extrusion (7) ofthe pulp is not essential to the implementation of the invention. Asimple addition of cryoprotectants in conventional manner is alsopossible. The pulping (1) can also be carried out in conventionalmanner. Likewise, the washing (2) of the pulp can be effected by othermeans provided that it enables the aforementioned fraction of between0.1 and 3% of lipids and sarcoplasmic proteins to be retained. Finally,the pulp draining operation (6) can be effected by pressing the pulp.

As already stated, the special feature of the invention is based on twoessential points which are now described in detail below and which, ifobserved conjointly, afford the industrial production of nutriment undersatisfactory economic conditions from “oily” fish of low commercialvalue.

1—Controlling the Oxidation and Denaturation Phenomena

The phenomena of denaturation and oxidation of the myofibrillar proteinsby the lipids or sarcoplasmic proteins are due to lipid/protein orprotein/protein interactions. The process according to the inventionmakes it possible firstly to limit the occurrence of these phenomena,and secondly to neutralize the elements that cause them.

The denaturation and oxidation of the myofibrillar proteins usuallystarts with the pulping operation. According to the invention, a volumeof water equivalent to at least a third of the volume of pulp used isadded to the pulp at the same time as the pulping operation with the aimof solubilizing the sarcoplasmic proteins as soon as possible andthereby limiting their oxidizing and denaturing action.

In conventional manner, the process water used throughout the processaccording to the invention, and therefore during the pulping operation,will be of high purity and at a temperature of between 0 and 10° C.Those skilled in the art will be able to adjust its pH so that the pulpremains as neutral as possible.

The residual lipids and sarcoplasmic proteins are then neutralizedduring the continuous mixing step—Phase 4. Intimate mixing of the pulp,with added water, during this operation will allow rapid diffusion ofthe water-soluble proteins and mechanical separation of the lipids,which form a stable aqueous emulsion. These elements are thusmicroencapsulated within the protein matrix. As any interaction betweenthe constituents of the mixture is prevented, the oxidation anddenaturation phenomena are neutralized.

Controlling these phenomena will make it possible to obtain ahigh-quality surimi throughout the year, irrespective of the specificcharacteristics of the fish used; this was not possible with the priorart. It will also make it possible to retain a residual fraction oflipids and sarcoplasmic proteins in the surimi-base and thereby toimprove the production yield, especially when the process is applied tothe production of surimi-base from oily fish.

2—Managing the Purification of the Pulp

As noted previously, the objective of the prior art was to remove all,or at least as much as possible, of the sarcoplasmic proteins, lipidsand impurities.

As will be seen, the invention makes it possible to remove theimpurities and odoriferous compounds while at the same time controllingthe removal of the lipids and sarcoplasmic proteins. The invention makesit possible to retain a greater or lesser fraction of these elementsaccording to the quality grade intended for the finished product.

According to the invention, removal of the unwanted elements starts withthe pulping operation—Phase 1.

In the process according to the invention, a gradation in the diameterof the sieve perforations is such that it is possible to distinguishbetween different fractions in the pulping operation according to thedensity of the material. This device has three major advantages.

Firstly, the recovery of the product can be optimized according to theintended quality grade. In other words, the choice can be made to retainone or more of the fractions of material according to the initialquality of the crude product.

Secondly, the impurities, such as the bones or skin, will be removedmore efficiently since they are obtained at the end of the separationrun, making it possible to improve the quality of the final product(whiteness of the surimi).

Finally, the fish fillets no longer need to be introduced manuallybecause this can be done by a continuous mechanized method using ahopper.

The pulp will then be washed and refined. It will be possible to adjustthe residual content of lipids and sarcoplasmic proteins by regulatingthe centrifugation parameters during the washing and refining.

Thus, during the centrifugation step (11), between 80 and 95% of theinitial amount of water used will be removed. This first choice allows afirst adjustment of the final content of lipids and proteins. Thecentrifugation step (11) according to the invention becomes one of theregulation points for the final quality of the product.

The final content of lipids and sarcoplasmic proteins will be adjustedduring the refining operation (Phase 3), this refining being effected ona pulp whose moisture content will have been chosen according to theintended quality grade by means of the separation mechanisms explainedabove. In the process according to the invention, the refining operationno longer serves only to wash the pulp; it becomes one of the regulationpoints for the quality of the final product. At this stage, theobjective of the invention is to retain a given fraction of these lipidsof between 0.2 and 1.5% of the total weight.

As has been seen, the process according to the invention affords a goodremoval of the impurities, providing those skilled in the art with aproduct having good characteristics while at the same time enabling themto retain a greater or lesser proportion of lipids and sarcoplasmicproteins whose oxidizing and denaturing capabilities have beenneutralized. To the Applicant's knowledge, neither this flexibility ofthe process, allowing adaptation to the nature and specificcharacteristics of the fish used and to the desired final quality of theproduct, nor the voluntary retention of lipids and sarcoplasmicproteins, is to be found in the prior art.

It will be seen in FIG. 3 that a yield of 30% is obtained for 0.2% ofmicroencapsulated lipids and a yield of 42% is obtained for 1.2% ofmicroencapsulated lipids.

Likewise, it will be seen in FIG. 4 that, up to a lipid content of 0.8%,there is no effect on the gelling strength of the surimi. It will benoted that high-quality gels are still obtained up to a content of 2.2%(boxed zone I in the Figure). The gelling strength gradient for 1.2% ofmicroencapsulated lipids is 68 N.mm⁻¹.

Apart from the major characteristics and advantages which have now beendescribed, the invention offers further advantages, especially in termsof the quality of the surimi produced.

For example, one of the advantages of the invention as regards thequality of the surimi produced is that it comprises an additional step,namely evacuation of the pulp—Phase 5—for specific removal of thevolatile compounds that are responsible in the prior art for the flavorof the product.

Another example relates to the criteria which the surimi-base has tosatisfy in respect of the gelling strength and the quality of the gelthat it will form after cooking.

Here again, the invention enables the quality of the surimi-baseproduced to be improved by carrying out a cold pulp extrusionoperation—Phase 7—at the end of the process.

Under the effect of the intense shear generated inside the extruder, thenative proteins will dissociate into monomers. The polypeptide chainswill unfold and expose the reactive groups that are the focal point ofhydrophobic reactions and the creation of disulfide bridges responsiblefor the organization of the proteins into a continuous and orderedthree-dimensional network.

Cold extrusion therefore makes it possible to improve the capabilitiesof the surimi-base to form a stable gel by increasing the number ofreattachment sites for the myofibrillar proteins, and to compensate forany degradation of these properties which the presence of residuallipids might have generated.

Finally, the extrusion operation means that no salt (or only a littlesalt) is required for protein reattachment, reducing the degradation ofthe pulp and enabling a smaller amount of cryoprotectant additives to beused.

Another advantage concerns the amount of water required for carrying outthe process. The processes of the prior art need several successiveadditions of water, with the result that up to five volumes of water areused to treat one volume of pulp. Some traditional techniques forprocessing oily fish can even result in the use of seven volumes ofwater for one volume of pulp. In the process according to the invention,three volumes of water will be used for one volume of pulp, therebyreducing the production costs.

Another advantage of the process according to the invention is that itcan run totally continuously from the introduction of the fish filletsinto the pulper up to the forming of the blocks.

As already emphasized, the invention is preferentially applied to thefield of the industrial production of surimi-base from “oily” fish.However, it is of course still applicable in a general manner to theproduction of surimi-base, or any other intermediate food product, fromany species of fish.

It is self-evident that the invention cannot be limited to this examplebut that it covers a multiplicity of variants or equivalent processessubject to compliance with the definition of the invention given in theattached claims.

1. A process for the manufacture of intermediate food products in a formof hydrated concentrates of myofibrillar proteins from fish flesh, saidprocess comprising the following steps: an initial pulp of minced fishflesh is prepared from fish fillets; said initial pulp is washed withwater to obtain a washed pulp containing a residual fraction of lipidsand sarcoplasmic proteins comprised between 0.1 and 3% of the weight ofthe pulp; said washed pulp is refined in the wet state by removing afraction of impurities; the refined pulp is mixed until it is in a formof a homogeneous emulsion; the emulsified pulp is drained to produce adensified pulp; cryoprotectants are added to the densified pulp to forma final pulp suitable for freezing; the final pulp is packaged in a formof blocks; and said blocks are frozen.
 2. The process as claimed inclaim 1, wherein the pulping operation is coupled with addition ofwater.
 3. The process as claimed in claim 2, wherein the water is addedin a ratio of at least one volume of water to three volumes of pulp. 4.The process as claimed in claim 1, wherein the pulping operation iscarried out as a function of a density gradient of fish fillets.
 5. Theprocess as claimed in claim 1, wherein the washing operation is composedof the following steps: water is added to the initial pulp and the wholeis mixed to form a water-pulp mixtures; the water-pulp mixture iscentrifuged and the resulting water is removed; and the centrifuged pulpis washed continuously with waters.
 6. The process as claimed in claim5, wherein in the centrifugation step, a volume of water removed isbetween 80 and 95% of a volume of water initially used.
 7. The processas claimed in claim 1, wherein the mixing operation is carried out untilthe homogenized pulp is in a form of an emulsion with a stability ofmore than 10 minutes.
 8. The process as claimed in claim 1, wherein themixing step is followed by a deodorization of the emulsified pulp inwhich the latter is evacuated.
 9. The process as claimed in claim 1,wherein the operation for draining the emulsified pulp is carried out bycentrifugal decantation.
 10. The process as claimed in claim 1, whereinthe final pulp is subjected to a cold extrusion operation duringaddition of cryoprotectants.
 11. An installation for carrying out theprocess as claimed in claim 1, comprising: a pulping device alsoprovided with a waste recovery trough (139); a pulp washing deviceprovided with a system for discharging the wash waters; a pulp refiningdevice provided with a system for discharging the fraction of impuritiesremoved; a continuous pulp mixing device; a pulp draining deviceprovided with a system for discharging the liquid fraction; a device foradding cryoprotectants to the pulp; a device for forming the pulp intoblocks; and a device for freezing the blocks.
 12. The installation asclaimed in claim 11, wherein the pulp pulping device comprises acylindrical sieve having perforations of different diameter according toa linear gradient ranging from 0.2 to 0.4 mm and a variable-pitchendless screw conveyor placed inside said sieve, which is providedupstream with a hopper.
 13. The installation as claimed in claim 11,wherein the washing device comprises: a refrigerated double-chamber tankequipped with a pipe for optional addition of water and with mixingequipment; a screen centrifuge; and a continuous washing devicecomprising of a refrigerated double-chamber cylindrical tank equippedwith a pipe for the addition of water, and with mixing equipment. 14.The installation as claimed in claim 11, wherein the pulp mixing deviceis a static continuous mixer of the LPD (low pressure drop) type. 15.The installation as claimed in claim 11, further comprising adeodorization device located behind the mixing device.
 16. Theinstallation as claimed in claim 11, wherein the pulp draining device isa centrifugal decantation device.
 17. The installation as claimed inclaim 11, further comprising a cold extrusion device allowing theaddition of cryoprotectants.
 18. The installation as claimed in claim11, wherein the cold extrusion device comprises: a conveyor of thehooded screw conveyor type; a controlled-throughput ram; and adouble-screw extruder equipped with means for monitoring and regulatingpressure.
 19. Surimi-base and other intermediate food products obtainedfrom oily fish by the process as claimed in claim 1, wherein a residualfat content is between 0.1 and 1.5%.
 20. Surimi-base and otherintermediate food products as claimed in claim 19, wherein the oily fishare sardine, scad, mackerel or sardinella.
 21. The process as claimed inclaim 2, wherein the pulping operation is carried out as a function of adensity gradient of the fish fillets.